A wide range of methods and apparatus are known and have been widely utilized in the fixed biological film aerobic treatment of aqueous liquors containing biodegradable waste products to provide a purified and safe effluent for return to the environment. As is known, the term "fixed film" refers to those systems where the microorganisms are attached to the surface of a solid inert material as opposed to being freely suspended as agglomerated particles in a liquid medium.
There are basically three general categories of fixed film aerobic treatment processes, a submerged system, in which the fixed film is submerged in aqueous liquor, a trickle bed system in which the fixed film is exposed to the atmosphere and aqueous liquors trickled over the film and a combination of the latter in which the fixed film is alternately immersed in an aqueous liquor and then exposed to air as is done in rotating biological contactors. In the submerged fixed film category the microorganisms can be attached either to the surface of immobile solid matrices or to mobile solid particles submerged in an aqueous liquor. In aerobic versions of submerged fixed film systems large volumes of air are bubbled through the mixture of aqueous liquor and fixed film microorganisms.
Representative patents which illustrate the submerged aerobic fixed film immobile matrix type systems for effecting biological oxidation of waste products are shown in the following patents.
U.S. Pat. No. 3,966,608 illustrates a submerged technique for biologically treating waste products. The treatment zone utilizes a central column and adjacent oxidation zones in fluid communication with the central column. An aerating fan is located at the top of the central column to draw the liquor upwardly through the central column and the aerated waste sprayed outwardly to effect aeration thereof and then caused to flow downwardly through the adjacent columns containing submerged packing, such as Raschig or Pall rings. The microorganisms which are fixed to the packing effect oxidation of the waste.
U.S. Pat. No. 3,235,234 illustrates a submerged technique for treating waste wherein a treatment zone is immersed in a tank containing waste, the treatment zone being filled with a porous packing such as saddles, wire mesh or corrugated sheets, defining a serpentine path in the vertical direction. An oxygenating gas is introduced through a diffuser, such as a sparge unit, placed beneath the packing. Both waste and oxygenating gas are forced upwardly through the packing unit and the waste biologically digested. The treated waste then overflows into the tank.
U.S. Pat. No. 4,231,863 illustrates the treatment of waste via a submerged technique. In that process a plurality of tubular materials are vertically extended within the treatment zone and an oxygenating gas introduced directly below the openings of each of the vertically extended tubes. The introduction of the oxygenating gas causes waste to flow upwardly through the tubes and then out and downwardly over the exterior surface of the tube, Micoorganisms supported on the tubes effect oxidation of the waste.
U.S. Pat. No. 3,563,888 and U.S. Pat. No. Re. 27,721 illustrate a variation in the submerged technique for waste treatment, such as described in U.S. Pat. No. 3,966,599 except that in the '888 case an oxygenating gas is introduced near the bottom of the central column thereby creating an airlift to circulate waste liquor.
Other examples of treatment systems are shown in U.S. Pat. Nos. 4,374,730; 4,045,344; 3,576,313; 3,773,660, 3,956,128; and 4,238,338.